1. Field of the Invention
The present invention relates to a data transmission method for a wireless network. More particularly, the present invention relates to a data transmission method with multiple token mechanism in wireless token ring protocol.
2. Description of Related Art
With development of wireless communication techniques, wireless networks have been widely used in our daily life. Since transmission lines are not required during wireless communication, the cost for constructing and maintenance of the transmission lines may be avoided.
Presently, an 802.11 standard has been defined by the institute of electrical and electronics engineers (IEEE). The 802.11 standard is widely used in different scenes of wireless communication. For example, in a coffee shop for afternoon tea, a user may communicate with others or surf on the Internet via a notebook computer and a wireless access point. However, the wireless access point has to be connected to the transmission lines for the user to connect the Internet. If a plurality of users is about to surf on the Internet simultaneously, the wireless access point may be used as a central controller, by which a medium access control (MAC) protocol of the 802.11 standard is applied in coordination with the wireless access point to avoid a collision during packets transmission.
Referring to FIG. 1 and FIG. 2, FIG. 1 is a schematic diagram of a MAC protocol of the 802.11 standard. FIG. 2 is a timing diagram illustrating a relationship of signals according to a MAC protocol of the 802.11 standard. In the 802.11 standard, the MAC protocol of the 802.11 standard is a contention MAC protocol, by which request-to-send (RTS) packets, clear-to-send (CTS) packets and network allocation vector (NAV) information are sent to avoid the collision of the transmission packets. When a node_1 is used for transmitting data to a wireless access point W_AP (node_1˜node_4 are wireless communication devices, for example notebook computers, personal digital assistants (PDAs), and cell phones etc.), the node_1 transmits the RTS packet and the NAV information (the NAV is packaged within the RTS packet, and is a header of the packet) to the wireless access point W_AP and other nodes, such as a node_3 and a node_4 within the signal coverage of the node_1, so as to notify the wireless access point W_AP, the node_3 and the node_4 there will be data to be transmitted, and the time required for transmission (by the NAV information). When the wireless access point W_AP receives the RTS packet, and after a waiting time of short inter frame space (SIFS), the wireless access point W_AP transmits the CTS packet and the NAV information (the NAV is packaged within the CTS packet, and is a header of the packet) to the node_1 from which the RTS packet is transmitted and the other nodes within the signal coverage of the wireless access point W_AP, such as the node_2, the node_3 and the node_4, so as to notify the node_1 that data transmission is permitted, and to notify the node_2, the node_3 and the node_4 that there will be data to be received, and the time required for receiving (by the NAV information). When the node_1 receives the CTS packet, and after the waiting time SIFS, the node_1 then transmits a data packet Data_A. When the wireless access point W_AP receives the data packet Data_A successfully, and after the waiting time SIFS, the wireless access point W_AP responds an acknowledgement (ACK) packet to the node_1, so as to notify the node_1 that transmission of the data packet Data_A to the wireless access point W_AP is successful. Next, after a waiting time of distributed inter frame space (DIFS), the node_1˜node_4 may contest with each other to determine which node may transmit the packets.
In FIG. 2, the node_2 is assumed to have successfully obtained a channel utilization privilege. The node_2 transmits the RTS packet and the NAV information (the NAV is packaged within the RTS packet, and is a header of the packet) to the wireless access point W_AP and to the node_3 and node_4 within the signal coverage of the node_2, so as to notify the wireless access point W_AP, the node_3 and the node_4 there will be data to be transmitted, and the time required for transmission (by the NAV information). When the wireless access point W_AP receives the RTS packet, and after the waiting time of SIFS, the wireless access point W_AP transmits the CTS packet and the NAV information (the NAV is packaged within the CTS packet, and is a header of the packet) to the node_2 from which the RTS packet is transmitted and the other nodes within the signal coverage of the wireless access point W_AP, such as the node_1, the node_3 and the node_4, so as to notify the node_2 that data transmission is permitted, and notify the node_1, node_3 and node_4 that there will be data to be received, and the time required for receiving (by the NAV information). When the node node_2 receives the CTS packet, and after the waiting time SIFS, the node_2 then transmits a data packet Data_B. When the wireless access point W_AP receives the data packet Data_B successfully, and after the waiting time SIFS, the wireless access point W_AP responds the ACK packet to the node_2, so as to notify the node_2 that transmission of the data packet Data_B to the wireless access point W_AP is successful. Next, after the waiting time DIFS, the node_1 node_4 may again contest with each other to determine which node may transmit the packet.
According to the MAC protocol of the 802.11 standard, a hidden node problem (i.e. the node_1 cannot be detected by the node_2) is solved, such that the packets collision is avoided. However, the MAC protocol of the 802.11 standard requires the wireless access point W_AP to work as the central controller, and the wireless access point W_AP has to be connected to a cable network. If such a network is constructed in a large area or in an outdoor environment, the cost of the construction will be huge.
Accordingly, a wireless mesh network using a wireless communication technique of multi-hop is provided. However, the multi-hop wireless mesh network can only be applied to a line topology, and the transmitted packet has to be a fixed length packet. For a network system applying a variable length packet, the variable length packet has to be cut and rearranged to form the fixed length packet. Therefore, signal-processing time during transmission is increased, and equipment cost is increased accordingly.
Moreover, a wireless token ring protocol (WTRP) is disclosed recently, and the WTRP allows the multi-hop communication technique to be applied to a ring topology. However, the WTRP may only provide one token to a certain node. In other words, each time only one node is permitted to transmit data, and therefore an output rate of the network system using the WTRP will be decreased due to the above reason.
To solve the aforementioned problems, a concept of spatial reuse for generating a plurality tokens is provided by the present invention, and the collision occurred during packets transmission among the plurality of nodes with the tokens, and the problem of the variable length packet cannot be transmitted can be avoided by applying a token elimination mechanism.